MONDAY, Nov. 19 (HealthDay News) -- A new study shows that lowered income actually has an inflammatory effect on the body, which may explain why people of lower socioeconomic status are at higher risk of heart disease, researchers report.

The link between higher levels of inflammatory molecules in the blood and lower income is weight gain, spurred by poor diet and lack of exercise, the study suggests.

"Lack of physical activity could be a factor, but it is less likely than diet," said study author Nalini Ranjit, an investigator at the University of Michigan School of Public Health.

The findings are published in the Nov. 20 issue of Circulation.

Ranjit and her colleagues studied data on more than 6,800 U.S. adults in the Multi-Ethnic Study of Atherosclerosis. With an average income of $51,000, 38 percent of the participants were white, 28 percent black, 22 percent Hispanic and 12 percent Chinese-American.

The researchers measured levels of two molecules found in the blood that are associated with inflammation -- interleukin-6 and C-reactive protein.

They found a direct relationship between levels of these inflammatory biomarkers and income.

Some people in the study made as much as $140,000 a year, Ranjit said, and people whose income was $41,300 below that figure had levels of IL-6 and CRP that climbed 6 percent to 9 percent higher compared to the top earners. The strongest association between income levels and inflammatory markers was seen among whites, she added.

Inflammation has long been linked to cardiovascular disease. It causes damage to blood vessels that can lead to blockage that results in heart attack, stroke or other cardiovascular problems.

While overweight was the single most important explanation for the link between lower socioeconomic status and a greater inflammatory burden, other factors did play a role, Ranjit said. "In an earlier paper, we showed that smoking played a role among blacks," she said. And a general attitude of "cynical distrust" was found to be associated with higher inflammatory molecule levels and lower levels of education, she added.

Diet is well known to affect other risk markers for cardiovascular disease, notably blood cholesterol levels, but levels of the inflammatory molecules "are more sensitive markers than serum [blood] cholesterol," Ranjit said.

Among both whites and blacks, a link between education level and inflammatory markers was also found. For example, a drop of 4.6 fewer years of education was associated with 6 percent to 14 percent higher levels of IL-6 and CRP.

"Our results suggest that persons of lower socioeconomic position have greater inflammatory burden than those of higher socioeconomic position because of the cumulative effects of multiple behavioral, psychological and metabolic characteristics," the researchers concluded. "If the role of inflammation in the origin of multiple chronic diseases is confirmed, inflammation may represent a common element through which socioeconomic position is related to cardiovascular disease and other chronic disease common in aging."

SOURCES: Nalini Ranjit, Ph.D., research investigator, University of Michigan School of Public Health, Ann Arbor; Nov. 20, 2007, Circulation